1. Field of the Invention
The present invention generally relates to methods of predicting mortality in patients with congestive heart failure, and more particularly to such methods including detection of hypothermia in a congestive heart failure patient. The invention also relates to apparatus, devices and kits for carrying out the methods.
2. Description of the Background Art
Congestive heart failure (CHF) is a leading, and increasing, cause of morbidity and mortality. Numerous predictors of mortality in patients with CHF have been described in the literature. For example, Myers et al.1 reports that in predicting outcome in severe chronic heart failure, peak oxygen uptake (VO2) surpassed clinical variables, right-heart catheterization data, exercise time, and other exercise test variables. Other prognostic variables have also been identified, including left ventricular ejection function (LVEF), age, creatinine, right ventricular ejection fraction (RVEF), hyponatremia, bilirubin and recently, lymphocyte count. Nevertheless, these variables together account for only a portion of the variance, with the strong predictors usually applying to only a few patients, leaving prognosis uncertain for the individual patient. The ability to accurately predict which patients are likely to have the shortest survival times is particularly needed in the selection of patients for heart transplantation or left ventricular assist device (LVAD) implantation. 2-19. An accurate prognosis helps physicians optimize therapies for their patients. Even if in the circumstances a more accurate prognosis would not improve therapy (e.g., when the therapy has already been optimized), most patients and their families want as accurate a prognosis as possible.
The invention contemplates a method, apparatus and kit devices for detecting a drop in a patient""s body temperature as a means of predicting imminent death in congestive heart failure patients.
In accordance with this invention, a method of monitoring a patient with congestive heart failure for prognosis of survival comprises: obtaining an initial body temperature which is not elevated above normal, then obtaining subsequent body temperatures of the patient and determining whether the subsequent temperatures fit any of predetermined criteria showing a condition of congestive heart failure hypothermia. A method of warning of imminent mortality in a patient suffering from congestive heart failure absent therapeutic intervention comprises sensing internal and/or external temperatures of a patient, analyzing the temperatures to determine a data set conforming to a predefined condition signifying congestive heart failure hypothermia; and issuing an alarm reporting said condition.
Such criteria include any one or more of: (i) a decrease in temperature of about 2xc2x0 F. or more from said initial temperature, (ii) a decrease in temperature of 1xc2x0 F. or more within a 12 hour period, (iii) a decrease in temperature of about 1xc2x0 F. or more over 24 hours if the patient""s mean temperature is at or below 96.5xc2x0 F., and (iv) a decrease in mean temperature of two standard deviations below the patient""s mean temperature over the prior 24 hours.
An embodiment of the method of the invention involving a graded or two-step manner of monitoring for risk of imminent mortality in a patient suffering from congestive heart failure, comprises (a) determining an initial body temperature which is not in excess of 97xc2x0 F., (b) obtaining subsequent body temperatures of the patient and determining whether the subsequent temperatures fit any of a first set of predetermined criteria for a condition of developing congestive heart failure hypothermia, and if so, (c) monitoring the patient under a second set of predetermined criteria for a developed condition of congestive heart failure hypothermia and determining whether the subsequent temperatures fit any of said second set of predetermined criteria, and if so; (d) triggering an alarm for intensive therapy.
A preferred embodiment measures the patient""s temperature at more than one site, analyzes the detected temperatures and triggers an alarm should a temperature decline be detected. In a particular of this method, the temperature gradient between the patient""s core and body surface is measured. In accordance therewith, a preferred method of the invention comprises (a) determining an initial body temperature which is not in excess of 97xc2x0 F., (b) obtaining at least one temperature sensor for measuring a cutaneous body temperature and at least one sensor for measuring a core body temperature; (c) positioning said sensors to be in direct contact with a patient having said initial temperature; (d) transmitting said core body temperature and said cutaneous body temperature at predetermined timed intervals to a processor programmed to analyze said temperatures; (e) analyzing said core body temperature and said cutaneous body temperature to determine if said temperatures fall outside of a predetermined criteria for a decrease in the patient""s temperature signifying a condition of congestive heart failure hypothermia; and (f) triggering an alarm if said temperatures fall outside of said predetermined criteria.
In one aspect the invention includes a method of monitoring a patient with congestive heart failure for prognosis of time remaining to death absent intervention, by obtaining an initial body temperature which is not elevated above normal, obtaining subsequent body temperatures of the patient and determining whether the subsequent temperatures fit any of predetermined criteria showing a condition of congestive heart failure hypothermia, and if so, predicting time to death according to the formula: time to death (hours)=12.5 (xc2x0 F. xe2x88x9295.24), where xc2x0 F. represents the current temperature of the patient.
The invention embodies apparatus, kits and temperature sensor devices for implementation of the invention. One such implement analyzes temperature measurements and comprises a processor programmed to activate an alarm if a temperature gradient between a core body temperature and a surface body temperature exceeds a predetermined criteria determined to signify congestive heart failure hypothermia.
A device useful in the present invention for monitoring body temperature preferably includes a temperature sensor for monitoring the core body temperature of the patient. Another useful temperature sensor comprises a temperature measuring device having means for notifying a patient diagnosed with congestive heart failure when the patient""s temperature decreases below a predetermined criteria.
In a greater particular, an apparatus useful in the practice of the invention includes a temperature detector for sensing temperature of a patient and generating a signal representative of the sensed temperature, a mount of said temperature sensor for indwelling or external placement on the patient, a data recorder for receiving said detector signals at timed intervals and using the signals to produce and store data representing temperatures of the patient sensed over time, an analyzer for processing said stored data to determine a data set conforming to a predefined condition signifying congestive heart failure hypothermia and outputting a signal indicative of the condition, and an alarm for receiving and reporting said output signal indicative of said condition. The apparatus can also include means of furnishing therapeutic warming to the patient.
It is further useful for the apparatus to include means providing one or more additional predictors including one or more of O2 saturation, PACO2, pH, respiratory rate, QRS width, R-R variability and T wave alternans, heart rate, blood pressure, pulse pressure and dP/dt, as a composite index to maximize sensitivity and specificity. Because most patients experience a fall in cardiac output and blood pressure before death (e.g. patients without known heart disease who are dying of sepsis, stroke, trauma, or failure of the kidneys, liver, or respiratory system) a temperature monitoring apparatus of the present invention augmented by e monitoring devices of the latter type also serves to warn of a risk of imminent death in these latter patients.
Yet another embodiment of the invention is a kit comprising a device having at least one temperature sensor for transmitting a signal indicative of the temperature of a patient with congestive heart failure, the means of receiving the signal indicative of the temperature of a patient and analyzing such signal to determine whenever the patient experiences a decline in temperature outside of a predetermined normal range, and a means for triggering an alarm if such a temperature decline occurs.